1. Field of the Invention
The present invention relates to a system for the delivery of inhalable medicament to a patient at a preset point in the breathing pattern of the patient. In particular, the invention relates to metered dose inhalers by means of which medicament may be delivered in metered doses.
2. Description of Related Art
It is well known to treat patients with medicaments contained in an aerosol, for example, in the treatment of respiratory disorders. It is also known to use for such treatment, medicaments which are contained in an aerosol and are administered to a patient by means of an inhalation device comprising a tubular housing or sleeve in which the aerosol container is located and an outlet tube leading out of the tubular housing. The aerosol containers used in such inhalation devices are designed to deliver a predetermined dose of medicament upon each actuation by means of an outlet valve member at one end which can be opened either by depressing the valve member while the container is held stationary or by depressing the container while the valve member is held stationary. In the use of such devices, the aerosol container is placed in the tubular housing with the outlet valve member of the container communicating via a support with the outlet tube, for example a nozzle or mouthpiece. When used for dispensing medicaments, for example in bronchodilation therapy, the patient then holds the housing in a more or less upright condition and the mouthpiece or nozzle of the inhalation device is placed in the mouth or nose of the patient. The aerosol container is pressed towards the support to dispense a dose of medicament from the container which is then inhaled by the patent.
It may be understood that effective delivery of medicament to the patient using an inhalation device as described above is to an extent dependent on the patient's ability to co-ordinate the actuation of the device (e.g. firing of the aerosol) with the taking of a sufficiently strong inward breath. For some patients the required co-ordination can present difficulties. Other patients, particularly those having severe respiratory problems, find it difficult to produce a reliable inward breath. Both of these sets of patients run the risk that they do not receive the appropriate dose of medicament.
Breath-actuable or breath-assisted inhalation devices have been developed to address the needs of patients having poor co-ordination skills and/or unreliable breath capability. Such devices typically have a breath trigger mechanism which triggers release of medicament in response to the inward breath of a patient.
One problem inherent with such breath-triggered devices is that a certain amount of the inward breath is used up before the trigger is activated. The full inward breath is thus, not available for inhalation of medicament. Further, that initial part of the inward breath which is ‘lost’ prior to release of the medicament is a relatively strong and inhalation-effective portion of the full inward breath. Where the patient has poor breath capacity the loss of this portion of the inward breath may significantly compromise the amount of medicament which is deliverable to the lungs.
Another problem with such breath-triggered devices is that the medicament may not be released at the optimum point in the breath cycle.
The Applicants have now found that enhanced delivery of medicament is achievable by use of a system in which the breathing pattern of a patient is monitored and drug release is coordinated with a preset point in the breathing pattern. This preset point is selected to optimise the delivery of drug to the lung. It has been found to be particularly advantageous if the preset point is defined relative to, or indeed to coincide with, the end of the exhalation part of the breath cycle.
The Applicants have also now appreciated that at the end of the exhalation part of the breath cycle, the patient's mouth cavity is typically at rest which allows it to act as a natural ‘spacer’ element, thereby assisting with dispersal of the delivered medicament. There is thus, potentially less need for the use of a separate mechanical spacer element as is commonly used in conjunction with the mouthpiece of conventional inhalation devices.